Implant for the delivery of electrical current to promote bone growth between adjacent bone masses

ABSTRACT

An electrical bone growth promotion apparatus for the delivery of electrical current to an implant surgically implanted between adjacent bone masses to promote bone growth to areas adjacent to the implant is disclosed. The apparatus of the present invention comprises a self contained implant having a surgically implantable, renewable power supply and related control circuitry for delivering electrical current directly to the implant and thus directly to the area in which the promotion of bone growth is desired. The desired areas of bone growth promotion may be controlled by conducting negative charge only to the desired location of bone growth promotion.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/631,309,filed Jul. 31, 2003, now U.S. Pat. No. 7,455,672, which is acontinuation of application Ser. No. 09/404,396, filed Sep. 23, 1999,now U.S. Pat. No. 6,605,089, which is a continuation of application Ser.No. 08/250,177, filed May 27, 1994, now U.S. Pat. No. 6,120,502, all ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to interbody bone fusion devices, and moreparticularly to an apparatus and method for the delivery of electricalcurrent to a spinal fusion implant and to interbody fusion material forinducing bone growth and aiding in spinal arthrodesis.

2. Description of the Related Art

The spine may be fused along any of its various surfaces, or internallywithin the interspaces of the vertebrae. Various interbody fusiondevices have been developed to promote interbody fusions of the spine,such as that of Michelson, U.S. Pat. No. 5,015,247, issued on May 14,1991, Brantigan U.S. Pat. No. 4,743,256, issued on May 10, 1988, andothers. Such devices have helped to achieve spinal fusion by providingstructural support, presenting bone promoting substances to the fusionsite, increasing the surface area available to participate in thefusion, and by being both self-stabilizing and stabilizing to a spinalsegment.

During normal bone repair, the area around the fracture of the boneexhibits negative charge. The application of electrical current tonegatively charge a site in which spinal fusion is desired simulates thebone's own normal repair process and promotes osteogenesis. Theapplication of electrical current to negatively charge a site in whichosteogenesis is desired, creates an electrochemical reaction(4e-+O₂+2H₂O—-->4OH⁻) which lowers the oxygen tension (decreasing theO₂) to stimulate osteoblastic activity and promote bone formation.Further, the formation of the hydroxyl radical (OH⁻) raises the localtissue pH which of itself is favorable to bone production and furtherpromotes increases in the presence of alkaline phosphatase, a verypotent stimulant of bone formation in its own right. Still further,there appears to be a direct effect of electrical current to present anegative charge at the cellular level so as to upset the restingelectrical potential of the cell membrane with a resultant electricalperturbation within the cell, the net effect of which is promotional tothe cellular activity of bone formation. Finally, the electromagneticfield generated by the passage of electrical current appears to beindependent of that current (on the basis of magnetism alone) to bepromotional of bone growth, though the mechanism remains unknown.

Conversely, the application of electrical current to positively chargean area of bone inhibits osteogenesis and thus inhibits bone formation.Therefore, the application of electrical current to deliver positivecharge to an area of bone may be used to control the bone fusion processso that it does not occur in undesired areas such as within the spinalcanal.

The bone fusion process is a race against time, for eventually, the bodywill give up its attempt to complete that process. Well-known within thefield of surgery is the use of electrical current delivered internally,or applied externally relative to a patient's body to promote bonegrowth and thus promote the bone healing or fusion process. However inregard to the spine, none of the interbody fusion devices of the pastincorporate the use of electric current to stimulate bone growth, toincrease the rate of osteogenesis and the spinal fusion process.

To date the use of electric current to promote bone growth in the spinalfusion process has taken two forms. The first is the use of aninternally implanted electrical pulse generator, with a cathode wireleading from the pulse generator being wrapped about a bone plugharvested from the patient's body which is then inserted into theintervertebral space. These devices however have been continuallyplagued with problems that include breakage of the lead wires from thegenerator to the fusion site and a second surgery to remove thegenerator implanted in the patient's body at a remote location to thefusion site after the service life of the battery has expired. The powersupplies of these implantable generators have been ineffective due totheir limited service life, which may be shorter than the time needed toattain solid fusion, and problematic due to the potential for tissuedamage in the event of a leak. The latter concern prompts mostphysicians to perform a second surgical procedure to explant thegenerator and internal battery supply. The additional surgery to explantthe device increases the risk of infection and danger to the patient,and results in unnecessary additional costs.

The second form in which electric current has been used in the past tostimulate spinal fusion required the wearing, external to the body ofthe patient, of an electromagnetic coil or coils. Unfortunately, neitherof these methods when utilized in conjunction with the known methods ofinterbody arthrodesis has proven fully effective.

Therefore, a need exists for the means and method of improving uponand/or perfecting the conjoined use of an improved interbody fusiondevice other than bone alone, and the promotion of bone growth withelectrical current.

SUMMARY OF THE INVENTION

The present invention is directed generally to an apparatus and methodfor the delivery of electrical current to a surgically implanted devicein a location in which bone growth is desired. More specifically, thepresent invention discloses an electrical bone growth promotion (EBGP)spinal fusion implant positioned within the intervertebral space betweentwo adjacent vertebrae of the spine to promote and induce bone growth inthe spinal fusion process. The EBGP implant of the present inventioncomprises a power supply and related control circuitry for deliveringelectrical current directly to the housing of the EBGP implant which issurgically implanted within the intervertebral space between twoadjacent vertebrae. The housing of the EBGP implant of the presentinvention is at least in part electrically conductive such that at leasta portion thereof serves as an active cathode to deliver negative chargedirectly to the spinal fusion site and to any bone material containedwithin the EBGP implant and thus directly to the area in which thepromotion of bone growth is most desired. As positive charges do notpromote bone growth, but actually induce resorption of bone, the areasof bone growth promotion may be controlled either by conducting onlynegative charges to the location for bone growth promotion is desired orby conducting negative charges to the area in which bone growthpromotion is desired and at the same time conducting positive charges toany area in which bone growth is to be inhibited. Thus, the housing or aportion thereof, serves as an active cathode for delivering negativecharge or a combination active cathode and active anode for deliveringnegative charge and for delivering positive charge, respectively, tobone mass.

As an electrical bone growth promotion apparatus, the EBGP implant ofthe present invention is not limited in its use with any particularspinal fusion implant. Many different embodiments of the EBGP implant ofthe present invention are possible. For example, in a first embodimentof the EBGP implant, an implantable power supply and related controlcircuitry are completely contained within a hollow central chamber ofthe housing of the EBGP implant such that the EBGP implant is aself-contained unit positioned within the intervertebral space betweentwo adjacent vertebrae of the spine and may deliver electrical chargedirectly to the fusion site to promote spinal arthrodesis. The powersupply and control circuitry may be contained in an extending portion ofa cap used to close one end of the hollow central chamber of the housingand thus may be inserted into the EBGP implant which itself may in theremainder be filled with bone.

The EBGP implant of the present invention is a self-contained unit whichovercomes the problems described above associated with the prior artdevices for delivering electrical current to promote bone fusion. TheEBGP implant of the present invention conducts electrical current viaits housing, or a portion thereof, to an area of bone adjacent to theEBGP implant in which the promotion of bone growth is desired. As nolead wires are present, the problem of breakage of such wiresexperienced by the devices of the past has been overcome. Further, asthe power supply and related control circuitry are fully containedwithin the EBGP implant of the present invention there is no need toimplant a power supply and/or said related control circuitry at a remotelocation from the EBGP implant. Further still, as the power supply andrelated control circuitry become entombed in the bone mass uponcompletion of the bone fusion process, no additional surgery is requiredto explant the power supply and/or control circuitry as was the casewith the prior art. Thus, as no explantation is required, thepossibility of infection to the patient and other risks inherent to allsurgical procedures are eliminated, while also substantially reducingthe costs of utilizing electric current to promote bone growth in thebone fusion process.

In a first variation of the first embodiment, the external housing ofthe EBGP implant, the threaded portion, or any part of the housing ofthe EBGP implant, may be utilized as an active cathode by coupling thecathode lead from the power supply and/or control circuitry containedwithin the EBGP implant to the housing or a portion thereof. Forexample, the housing may be a spinal fusion implant such as thatdescribed by Michelson in U.S. Pat. No. 5,015,247, issued on May 14,1991, and could utilize its continuous external thread much like a woundcoil with the threaded portions being separated from one another andfrom the remainder of the spinal implant by an electricallynon-conductive ceramic material, and further that non-conductivematerial itself may also be osteoinductive.

In a second variation of the first embodiment, the housing of the EBGPimplant further includes an opening through which bone growth from onevertebra to a second adjacent vertebra may occur. Coaxial with theopening is a coil that is coupled to the cathode lead of the powersupply. The coil acts as an active cathode to deliver a negative chargeand promote bone growth through the opening and coil. In a furthermodification of this variation the cathode continues as a coil about thehousing of the EBGP.

In a second embodiment of the EBGP implant of the present invention, anyof a number of already known or conventional surgically implantablepower supply units and related control circuitry may be placed withinthe body of the patient at a location remote to the spine. A lead wirecouples the power supply and/or control circuitry to the housing of theEBGP implant, such as a spinal fusion implant, situated within theintervertebral space between and in contact with two adjacent vertebrae.The EBGP implant which is at least in part not made of bone, and thatpart also being electrically conductive, is used to conduct electricalcurrent to the interbody spinal fusion mass. In one variation of thesecond embodiment, the entire housing of the EBGP implant iselectrically conductive and functions as an active cathode to delivernegative charge to the area of bone adjacent thereto. In a secondvariation of the second embodiment, the housing of the EBGP implant maybe made of a combination of electrically conductive and non-conductivematerials such that a first portion of the housing of the EBGP implantis an active cathode specifically utilized for the delivery of thenegative electrical charge as discussed above for the first variation ofthe first embodiment and a second portion of the housing is an activeanode specifically utilized to deliver positive charge to the area inwhich bone growth is not desired. The area of the anode may be minimizedto reduce the area in which bone growth is inhibited or may be largersuch that the anode is used to prevent bone formation over a substantialarea.

In order to make efficient use of the power supply, rather thanconducting electrical current to the entire housing of the EBGP implantof the present invention which would require a large power supply,electrical current may be conducted only to the threads of the housingor to a wire coil insulated from the remainder of the housing. In thismanner less current is drained from the power supply without reducingthe effectiveness of the electrical charge delivered to the site inwhich bone fusion is desired since the electrical field created aboutthe coil or threads extends beyond the coil of the threads.

In a third embodiment of the EBGP implant of the present invention, aspinal fusion implant is preferably implanted surgically within theintervertebral space between two adjacent vertebrae and is wholly orpartially ferromagnetic. The spinal fusion implant is hermeticallysealed in a jacket composed of a non-ferromagnetic, biocompatiblematerial which may or may not be electrically conductive. Anelectromagnetic field is produced by an electromagnetic coil or coilsworn external to the patient's body. The spinal fusion implant may beinductively coupled to the electromagnetic fields generated andtransmitted by the external coils, and thereby generate its ownelectromagnetic field and accompanying electrical currents. Theseinternal fields and currents are localized within that segment of thespine in which the spinal fusion implant is located, and will inducebone growth and promote the spinal fusion process.

In a first variation of the third embodiment, the EBGP implant is whollyor partially powered by electrical currents induced within the EBGPimplant by the externally-applied electromagnetic fields. Likewise, anybattery source integrated into the EBGP implant may be recharged viasuch electromagnetic induction to renew the service life of the batterysource and thus extend the period of time in which bone growth may beelectrically promoted. The EBGP implant in this embodiment deliverselectrical current and replenishes the power supply when inductivelycoupled to externally applied electromagnetic fields.

In another embodiment of the EBGP implant of the present invention, thepower supply is surgically implanted within the body of the patient, butat a location remote to the spine such as a subcutaneous implantation,and is rechargeable in response to the application of external magneticfields.

In still another embodiment of the EBGP implant of the presentinvention, the battery source is charged by an external power source byferromagnetic induction and continues to deliver charges via thatbattery source even after the activity of the external coil ceases.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide an electrical bonegrowth promotion implant in which a power supply, related controlcircuitry, and delivery system are entirely self-contained within aspinal fusion implant, thus eliminating the need to violate other bodytissues to situate the implant, thereby limiting the extent of surgery,the time for surgery, the blood loss, and the risk of infection;

It is another object of the present invention to provide an electricalbone growth promotion implant for delivering electrical current topromote bone growth in a biomechanically and biophysiologically optimalplace so as to induce spinal fusion within the compressive weightbearing axis of the spine;

It is yet another object of the present invention to provide anelectrical bone growth promotion implant that eliminates the need forlead wires, the breakage of which has historically been a major sourceof failure in regard to the use of electrostimulators in general;

It is a further object of the present invention to provide an electricalbone growth promotion implant in which with successful arthrodesis, theencapsulated power supply and/or related control circuitry becomespermanently entombed in the bone fusion mass thus eliminating the needto perform a second surgical procedure for its removal;

It is still a further object of the present invention to provide anelectrical bone growth promotion implant in which an active cathode isfully contained within the bone fusion mass;

It is another object of the present invention to provide an electricalbone growth promotion implant in which the power supply and/or relatedcontrol circuitry combined is an internal extension of either a spinalfusion implant itself or of an insertable cap of the spinal fusionimplant;

It is a further object of the present invention to provide an electricalbone growth promotion implant which will receive externally appliedelectromagnetic fields and thereby generate electromagnetic fields andelectric currents affecting the bone within and adjacent to the spacebetween two adjacent vertebrae; and

It is yet a further object of the present invention to provide anelectrical bone growth promotion implant in which the power source fordelivering electric current to the implant is wholly or partiallysupplied or recharged by externally applied electromagnetic fields.

These and other objects of the present invention will become apparentfrom a review of the accompanying drawings and the detailed descriptionof the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded elevational side view, partially in cross section,of the electrical bone growth promotion implant of the presentinvention.

FIG. 2 is an elevational side view, partially in cross section, of theelectrical bone growth promotion implant of the present inventioninserted between two adjacent vertebrae of the spine.

FIG. 3 is an alternative embodiment of the cap used for closing the openend of the electrical bone growth promotion implant of the presentinvention.

FIG. 3A is an enlarged fragmentary view along line 3A of FIG. 1 showingin cross section the end of the casing.

FIG. 4 is a side elevational view, partially in cross section, of afirst alternative embodiment of the electrical bone growth promotionimplant of the present invention having one end in which a portionthereof is made of a non-conductive material and insulated from the restof the implant such that different polarities of electrical charges maybe delivered to different parts of the implant as illustrated by theelectrical field arrows.

FIG. 5 is an end view of the electrical bone growth promotion implant ofthe present invention along line 5-5 of FIG. 4.

FIG. 6 is a cross sectional, side elevational view of a secondalternative embodiment of the electrical bone growth promotion implantof the present invention having a cap at one end in which a portionthereof is made of non-electrically conductive material.

FIG. 7 is a side elevational view of a third alternative embodiment ofthe electrical bone growth promotion implant of the present inventionhaving outer threaded portions that are separated from the rest of theimplant by a non-electrically conductive insulating material.

FIG. 8A is an enlarged fragmentary cross sectional view of the thirdalternative embodiment of the electrical bone growth promotion implanttaken along line 8 of FIG. 7 showing the threaded portion being anchoredto the non-electrically conductive material.

FIG. 8B is an enlarged fragmentary cross sectional view of the thirdalternative embodiment of the electrical bone growth promotion implanttaken along line 8 of FIG. 7 showing the thread portion being anchoredto and passing through a non-conductive material.

FIG. 9 is a side elevational view of a fourth alternative embodiment ofthe electrical bone growth promotion implant of the present inventionhaving an external wire coil interposed between the external threads ofthe implant and insulated from the remainder of the implant by annon-electrically conductive insulating material.

FIG. 10 is an enlarged fragmentary view taken along line 10 of FIG. 9showing the external wire coil being held in place between the externalthreads of the implant by a non-electrically conductive insulatingmaterial.

FIG. 11 is a perspective view of a fifth alternative embodiment of theelectrical bone growth promotion implant of the present invention havingan opening surrounded by a wire coil coaxial with the openingelectrically connected to a remote power source.

FIG. 12 is a side view of a sixth alternative embodiment of theelectrical bone growth promotion implant of the present invention havingan opening surrounded by a wire coil coaxial with the opening andelectrically coupled to an internal power source.

FIG. 13 is a top plan view of the electrical bone growth promotionimplant of FIG. 12 showing the opening.

FIG. 14 is a cross sectional side elevation view along lines 14-14 ofFIG. 11 of the bone growth promotion implant of the present inventionhaving an external power source and illustrating the bone growth fromone vertebra to a second adjacent vertebra that occurs during the spinalfusion process.

FIG. 15 is a perspective view of a structural support member used tosupport a wire coil coaxial with the vertical opening of the electricbone growth promotion implant of the present invention.

FIG. 16 is a cross sectional side elevational view of a seventhalternative embodiment of the electrical bone growth promotion implantof the present invention having an insulated cap at one end, a cathodelead from an external power supply connected to.

FIG. 17 is an end view of the seventh alternative embodiment of theelectrical bone growth promotion implant along 17-17 of FIG. 16.

FIG. 18 is a front elevational view of an externally wornelectromagnetic energy transmitter for transmitting an electromagneticfield to an implanted spinal fusion implant.

FIG. 19 is a cross sectional view taken along lines 19-19 of FIG. 18illustrating the transmission of electromagnetic energy generated by theelectromagnetic energy transmitter to a spinal fusion implant positionedwithin the patient's spine.

FIG. 20 is a perspective side view of an eighth alternative embodimentof the electric bone growth promotion implant of the present inventionhaving an internal power supply and generator shown in hidden line.

FIG. 21 is a perspective view of a ninth alternative embodiment of theelectric bone growth promotion implant of the present invention havingan internal power supply and generator shown in hidden line.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, the electrical bone growth promotion (EBGP)implant of the present invention is shown and is generally referred toby the numeral 10. In the preferred embodiment, the EBGP implant 10comprises a housing 30 as shown in FIG. 2 which is implanted in theintervertebral disc space S between adjacent vertebrae V₁ and V₂ in asegment of the spine for achieving arthrodesis.

As shown in FIG. 1, housing 30 includes a hollow tubular body that is atleast partially cylindrical having side walls 34 and preferably made ofan surgically implantable and electrically conductive material such as,but not limited to, titanium. The housing 30 has a hollow centralchamber 36 that is open at its distal end 38, is closed at its proximalend 40 and has a series of macro-sized openings 42 perforating the sidewalls 34. The macro-sized openings 42 preferably have a diameter in therange of approximately 2.0 mm to approximately 6.0 mm to allow for themacro fixation of the adjacent vertebrae V₁ and V₂. During the fusionprocess, bone growth occurs from each of the two adjacent vertebrae V₁and V₂ through the macro-sized openings 42 to any natural or artificialbone fusion enhancing material that may be contained within the centralchamber 36 so as to form a single solid mass.

The housing 30 has a similar structure and configuration of a spinalimplant such as, but not limited to, the spinal fusion implant taught byMichelson in U.S. Pat. No. 5,015,247. The housing 30 is preferably, atleast in part, electrically conductive and is made of material strongerthan bone to provide structural support to the two adjacent vertebrae V₁and V₂ while awaiting bone ingrowth, becoming firmly and permanentlyfixed in place once bone growth has occurred. To further enhance bonegrowth, the housing 30 may be coated with a bone growth inducingmaterial such as, but not limited to, hydroxyapatite, hydroxyapatitetricalcium phosphate, bone morphogenic protein and the like. The housing30 may also have a surface configuration that enhances bone growth suchas, but not limited to surface knurling or roughening.

The open distal end 38 has internal threads 39 and is closeable with acap 50 having at least a portion thereof that is electricallyconductive. The cap 50 has a threaded end 52 which is threaded to matchthe internal threads 39 and secured to internal threads 39 by the use ofa driver/wrench W or an equivalent tool.

Attached to and extending from the cap 50 is a casing 80 for containingelectrical components discussed in greater detail below. The casing 80is appropriately sized such that it fits within the central hollowchamber 36 of the housing 30 and occupies the least amount of spacepossible so as to limit interference with the bone fusion process. Whenthe cap 50 is threadably coupled to the housing 30, the casing 80 iscompletely contained within the central hollow chamber 36 such that theEBGP implant 10 is a self-contained unit.

Referring to FIG. 2, the EBGP implant 10 is shown surgically implantedin the disc space S between the two adjacent vertebrae V₁ and V₂. Atleast a portion of the housing 30 is embedded into the bone of theadjacent vertebrae V₁ and V₂. However, it is appreciated that for thepurpose of the present invention, the housing 30 need not be embeddedinto the bone of the vertebrae V₁ and V₂, but need only be placedadjacent to and be in contact with the vertebrae V₁ and V₂ in order toenable the EBGP implant 10 to conduct electrical current to the adjacentvertebrae V₁ and V₂.

It is to be understood that electrical current is a function of the timerate of change of electrical charge and the terms current and charge maybe alternatively used depending upon context in describing the EBGPimplants of the present invention. Further, as charge is proportional tothe resistance encountered by the current, as bone growth occurs theresistance encountered by the current delivered to the bone mass will beincreased, such that the charge will decrease. Also as the power supplydepletes, the amount of current delivered over time will also decrease.

The hollow central chamber 36 can be filled with and may hold anynatural or artificial osteoconductive, osteoinductive, osteogenic, orother fusion enhancing material. For example, bone material B harvestedfrom the patient may be loaded into the central hollow chamber 36 aswell as packed around the exterior of the housing 30, but within theintervertebral disc space S, wherein it is utilized in the spinal fusionprocess. An obdurator or similar instrument may be used to create aspace in the bone material B for receiving an object therein such as thecasing 80. In this manner, the housing 30 may be filled with bonematerial B and then closed with the cap 50 to hold the bone material Bwithin the hollow chamber 36 during surgical implantation.

The casing 80 itself, or a portion thereof, is made of an electricallyconductive and surgically implantable material such as, but not limitedto, titanium such that electrical current applied to the casing 80 maybe transferred from the casing 80 to the bone material B that iscontained within the hollow central chamber 36. The casing 80 may beremovably attached to the cap 50 or may be permanently affixed. In thepreferred embodiment, the casing 80 is electrically coupled to the cap50. However, it is appreciated that the casing 80 may be electricallyinsulated from the cap 50 if it is not desired to conduct an electricalcurrent to the cap 50 or if it is desired to conduct an electricalcurrent to the cap 50 having a different polarity from the remainder ofthe casing 80.

Within the casing 80 are the electrical components comprising a powersupply 60, control circuitry 70, a cathode lead 72, and an anode lead74. Both the power supply 60 and the control circuitry 70 are fullyimplantable and hermetically sealed. The cathode lead 72 is electricallycoupled to the cap 50 either directly or via the casing 80, such thatwhen the cap 50 is threaded to the housing 30, negative electricalcharge is transferred to the housing 30 such that the housing 30 itselfbecomes an active cathode. In this manner, the power supply 60 iselectrically coupled to the housing 30 and is located at the site inwhich spinal fusion is desired. Thus, in this embodiment, the EBGPimplant 10 is a self-contained unit, thereby eliminating the need toimplant the power supply 60 and related control circuitry 70 at a remotelocation within the patient's body, as is the case with fusionstimulators of the prior art.

The control circuitry 70 preferably includes well known means for thedelivery of a constant current source, providing a single, presetcurrent in the range of 0.01 to 20 uA. Thus, neither attachment ofmultiple cathodes or variation in cathodic area will alter the currentdensity delivered to the bone fusion mass. It is appreciated that thecontrol circuitry 70 may also include a wave form generator, a voltagegenerator or a clock means for delivering intermittent pulses of currentwith out departing from the scope of the present invention.Alternatively, the control circuitry 70 may comprise means for providingvarious patterns of direct current, alternating current, pulsatilecurrent, sinusoidal current, or electrical noise generated by currentrather than constant, direct current in order to promote bone growth. Itis further appreciated that the electrical components may also compriseany of the well-known devices currently available to electricallystimulate spinal fusion, such as but not limited to the stimulatoravailable from EBI Medical Systems, Parsippany, N.J., and may also beany of the devices suitable for delivering electric current and suitablefor implantation well-known by those skilled in the art.

The control circuitry 70 is powered by the fully implantable,hermetically sealed power supply 60 which may be any of the well-knownpower supplies known in the art and currently commercially available andused to electrically promote spinal fusion such as, but not limited to,the power supply by EBI Medical Systems, Parsippany, N.J. The powersupply 60 also may contain circuitry for generating electrical charge inresponse to externally applied electromagnetic fields.

Referring to FIG. 3, alternatively, the power supply 60′ may includebattery recharge circuitry responsive to externally appliedelectromagnetic fields for recharging the battery. As a consequence, theoverall size of the power supply 60′ may be substantially reduced with acorresponding reduction in the size of the casing 80′. In this manner,any interference with the bone fusion process by the casing 80′ isfurther reduced. Moreover, the longevity of the power supply 60′ may besubstantially increased as the power supply 60′ may be recharged toextend its life beyond that of a conventional non-rechargeable batteryhaving a fixed service life. As a result, the electric promotion ofosteogenesis may be extended beyond the service life of conventionalprior art devices with their non-rechargeable batteries. Further, therechargeable power supply 60′ may be reduced in size as the service lifemay be extended indefinitely, compactness of power supply such that bonegrowth promoting bone material is not displaced which is essential forfusion.

Also shown in FIG. 3, is an alternative embodiment of the cap 50′ whichmay be secured to the housing 30 by a spring fastening means 52′ whichengages the interior surface of the housing 30 once the spring fasteningmeans 52′ is inserted in the central hollow chamber 36. In thisembodiment, the time required to load bone material B within the centralhollow chamber 36 and the time to assemble the cap 50′ to the housing 30is significantly reduced.

As shown in FIG. 3A, the end of the casing 80 includes an insulatedscrew 90 made of a non-conductive material. The screw 90 has a threadedportion 92 which threadably attaches to the casing 80, and has anelectrically conductive core 94 passing through the longitudinal axis ofthe screw 90. The electrically conductive core 94 terminates at one endinto an electrically conductive head portion 96 and is at its other endelectrically coupled to the anode lead 74. In this manner, the headportion 96 becomes the active anode for delivering positive electricalcharge to an area of bone. As previously noted positive electricalcharge inhibits osteogenesis, the head portion 96 preferably has thesmallest possible size to limit the area of contact to bone exposed topositive charge to limit bone resorption and is positioned at a locationwhere the presence of positive charge will least interfere with thefusion process.

In the preferred embodiment, the head portion 96 is located at the tipof the end of the casing 80 such that when the cap 50 is attached to thehousing 30, the head portion 96, and thus the active anode, is at alocation which least interferes with the electrical promotion of thebone material B contained with the central chamber 36 and hassubstantially no contact with the adjacent vertebrae V₁ and V₂ to whichfusion is desired. An example of the electrical current present in theEBGP implant 10 is illustrated by the electrical field arrows in FIG. 2.

As the promotion of bone growth occurs by the application of negativeelectrical current, the promotion of bone growth may be controlled bythe application of negative electrical current only to the location inwhich bone growth is desired. For example, if bone growth promotion isdesired at a particular location, negative current may be transferred tothe housing 30 or a portion thereof which is adjacent to and in contactwith a desired site in order to accelerate the fusion process. In areaswhere bone growth is not desired, such as near the canal of the spinefor example, positive current may be transferred to the desired site.

Referring again to FIG. 1, in order to conduct positive charge from thehead portion 96 (the active anode) the presence of which is undesiredwithin the central hollow chamber 36, an insulated screw 20 having aconductive inner core 22 is threaded through an opening 24 in theproximal end 40. The insulated screw 20 has a recess 26 for receivingand coupling to the head portion 96. In this manner, positive charge isconducted by the conductive inner core 22 to a point external to thehousing 30.

Referring to FIGS. 4 and 5, a first alternative embodiment of the EBGPimplant is shown and generally referred to by the numeral 110. The EBGPimplant 110 comprises a housing 130 similar to the housing 30 describedabove, except that it has a proximal end 140 that is at least in partinsulated from the remainder of the housing 130. The housing 130 hasmacro-sized openings 142 to permit bone growth therethrough. Anode lead174 from the power supply 160 and/or control circuitry 170 may beelectrically coupled to the proximal end 140 of the housing 130 so thatthe proximal end 140 may be positively charged. To accomplish this, theproximal end 140 has a screw 120 having a conductive screw head 121, aconductive inner core 122, and an insulated stem portion 123 having arecess 126 for coupling to the head portion 196 (the active anode.) Theinner core 122 conducts positive charge from the head portion 196 to theconductive screw head 121. The screw head 121 is insulated from thehousing 130 by an insulated ring 125 made of a non-electricallyconductive material so that the screw head 121 can conduct positivecharge to a point external to the housing 130 so that at least a portionof the proximal end 140 of the housing 130 becomes positively charged asillustrated by the electrical field arrows in FIG. 4. In this manner,the area of positive charge may be varied in size by varying the area ofthe screw head 121, and thus the area of potential promotion of boneresorption is also variable. As shown in FIG. 4, the area of screw head121 has been deliberately increased to inhibit bone formation in an areaadjacent to the screw head 121.

The configuration of electrical charges shown in the EBGP implant 110would be utilized when the housing 130 is installed from the posterioraspect of the spine toward the anterior aspect of the spine since theproximal end 140 of the EBGP implant 110 would be proximate to thespinal canal once implanted in the disc space S between two adjacentvertebrae V₁ and V₂. By conducting positive charges to the proximal end140 osteogenesis in the spinal canal which could compress the neuralstructures is inhibited.

It is appreciated that where negative electrical charge for the purposeof promoting bone growth is desired generally along the entire EBGPimplant 110, then the positively charged screw 120 would have a screwhead 121 proportionally much smaller in size to limit the area ofpositive electrical charge.

For the areas adjacent to the housing 130 in which bone growth andfusion is desired, the cathode lead 172 from the power supply 160 and/orcontrol circuitry 170 is coupled to the casing 180 and negative chargesare conducted to the housing 130 by the contact of the casing 180 andcap 150 with the housing 130 such that the housing 130 itself becomes anactive cathode.

It is further appreciated that the delivering of positive charges andthe negative charges may be reversed simply by interchanging the anodelead 174 and the cathode lead 172 coupling points to the housing 130,cap 150, distal end 140, or screw 120. In this way, negative charge maybe applied and directed only to the particular areas in which bonegrowth is desired depending on the type of surgery, bone growth, andfusion desired.

Referring to FIG. 6, for example, if the EBGP implant 110 is installedfrom the anterior aspect toward the posterior aspect of the spine, thedistal end 138 of the housing 130 would be proximate to the spinalcanal. In order to prevent undesired bone growth near the spinal canal,the distal end 138 of the housing 130 or a portion thereof, which whenimplanted is adjacent to and in contact with the bone near the housing130, may be insulated from the remainder of the housing 130. Further,the distal end 138 may be positively charged by being connected to theanode lead 174 of the generator 160 so that the proximal end 138 itselfserves as an active anode. This can be accomplished by having aninsulated screw 156 having an electrically conductive core 158. Theelectrically conductive core 158 becomes the active anode and deliverspositive electrical charge to the adjacent bone area. Thus, bone areaadjacent to and in contact with the distal end 138 would be exposed onlyto positive charge and not to bone growth promoting negative charge.Further, in order to minimize bone resorption, the diameter of theelectrically conductive core 158 may extend from the insulated screw 156and may be decreased in size to limit the bone area being exposed topositive electrical charge.

The application of different polarity charges to different areas of thehousing 130 may also be accomplished by having the threads 152 of a cap150 coated with a non-conductive material such as, but not limited to, aceramic material in order to insulate the cap 150 from the remainder ofthe housing 130 such that the cap 150 becomes the active anode whenconnected to the anode lead 174 and is positively charged. This willprevent electrical promotion of bone growth in the vicinity of the cap150 which is adjacent to the spinal canal and in contact with the bonenear the spinal canal when implanted. However, it is appreciated thatother means of insulating the distal end 138 well-known by those skilledin the art, may be employed so that the distal end 138 has a differentcharge than the remainder of the housing 130 or has no charge at all.

Referring to FIGS. 7, 8A and 8B, a second alternative embodiment of theEBGP implant of the present invention is shown and generally referred toby the numeral 210. The EBGP implant 210 comprises a housing 230 similarto the housing 30 described above. The exterior of the housing 230 hasexternal threads 200 which are formed on the outer circumference of thehousing 230 preferably in a helix.

As shown in FIG. 8A, the threads 200 of the housing 230 are electricallyconductive and have a non-conductive insulating material 202 separatingthe threads 200. The insulating material 202 may be ceramic orpolyethylene or any other biocompatible material that has electricalinsulating properties. In this second alternative embodiment, thehousing 230 may be completely or partially hollow and threads 200 serveas the active cathode to conduct negative charge to the bone area inwhich the housing 230 is implanted and any material that may be withinthe housing 230. As the insulating material 202 is interposed betweenthe threads 200 themselves and between the housing 230 itself, thethreads 200 are isolated from the remainder of the housing 230 andessentially act as a coil that surrounds the exterior of the housing230. The threads 200 are electrically connected to the cathode lead 74(see FIG. 1) of the control circuitry 70 described above and thus thethreads 200 function as a cathode to deliver negative charge from theEBGP implant 210 to the vertebrae V adjacent to the housing 230 andmaterial contained within the housing 230 if any. The advantage of thisarrangement is that only the coil threads 200 are charged rather thanthe external housing 230 and since the beneficial electrical effect tosome instance from each of the threads 200, the threads 200 are aneffective cathode lead with less current drain than would be required tocharge the external housing 230.

As shown in FIG. 8B, it is possible to configure the threads 200 suchthat at least a portion thereof passes through the insulating material202 and communicates with the central chamber 236 so as to also conductelectric charge to any material contained within the housing 230 asillustrated by the electrical field arrows. This design requires thateither the inward or outward portions of the threads 200 not becontinuous such that the integrity of the housing 230 is notsubstantially reduced. The housing 230 has macro-size openings 242 topermit bone-growth therethrough.

Referring to FIGS. 9 and 10, a third alternative embodiment of the EBGPimplant 310 of the present invention is shown and is generally referredto by the numeral 310. In the third embodiment, the EBGP implant 310comprises a housing 330 similar to the housing 30 described above,having threads 300 and a wire 350 placed between the threads 300. Thewire 350 is supported by a non conductive insulating material 364 thatis placed between the threads 300 of the housing 330. The insulatingmaterial 364 has a groove 362 for receiving and holding the wire 350.The wire 350 is electrically coupled to a cathode lead such as thecathode lead 72 of the generator 60 (shown in FIG. 1) and is negativelycharged such that wire 350 conducts bone growth promoting negativecharge to the bone area of the adjacent vertebrae V₁ and V₂ adjacent tothe coiled wire 350 and through the openings 342 to the fusion masswithin the housing 330. The insulating material 364 prevents the body ofthe housing 330 from becoming electrically charged and preventselectrical conduction between wire 350 and threads 300 and housing 330and any short circuiting of the coiled wire 350. In this manner, thearea of the EBGP implant 310 which is electively charged is limited tothe coiled wire 350 to significantly reduce the total area which iselectrically charged. However, as the coiled wire 350 essentiallyextends approximately the entire longitudinal length of the EBGP 310, itis possible to deliver electrical charge to the entire area of boneadjacent to the EBGP 310 to stimulate bone growth without any diminishedeffect. Thus, the EBGP implant 310 is energy efficient since the amountof electrical current required to power the EBGP implant 310 issubstantially less than that required for an implant where the entireimplant housing is charged.

Referring to FIGS. 11-15, a fourth alternative embodiment of the EBGPimplant 410 of the present invention is shown and is generally referredto by the numeral 410. In the fourth embodiment, the EBGP implant 410comprises a housing 430 similar to the housing 30 and having an opening420 having an axis that is perpendicular to the longitudinal axis L ofthe housing 430. The opening 420 passes through the housing 430 andcommunicates with the central chamber 436 of the housing 430 and issurrounded by four structural support members 421, 422, 423, and 424.The opening 420 is covered by a lattice 415 at both ends. The lattice415 has openings 416 sufficiently sized to permit bone growththerethrough yet remains capable of retaining any natural or artificialbone growth material that may be contained within the hollow centralchamber 436.

Referring to FIG. 15, an enlarged perspective view of structural supportmember 421 is shown. Each of the structural support members 421, 422,423, and 424 are identical such that the description of one applies toeach of the others. The structural support member 421 made of anelectrically non-conductive material, has an upper arm 440 and a lowerarm 442 that are placed in the hollow central chamber 436 and aresecured to the spinal implant 410; a central portion 443 having a curvedouter edge 444; and a grooved inner edge 446. The inner edge 446 of thestructural support member 421 has a plurality of grooves 448 forreceiving and holding a wire 425 capable of conducting electricalcurrent. The plurality of grooves 448 are offset from each other andfollow the curvature of the outer edge 444 of the structural supportmember 421.

Referring back to FIG. 11, preferably the four structural supportmembers 421-424 are arranged around the outer perimeter of the opening420 such that they are equidistant from one another. The wire 425 isplaced within the grooves 448 and coiled about the four structuralsupport members 421-424 to form a wire coil 426 around the perimeter ofthe opening 420 substantially along the entire vertical length of theopening 420 that is coaxial with the opening 420.

The wire coil 426 is electrically coupled to a cathode lead 472 anddelivers and delivers a negative charge to the area surrounding withinthe torroid opening 420 such that bone growth is promoted and stimulatedby the presence of negative charge along the inner and outer walls ofthe torroid shaped wire coil 426. When the EBGP implant 410 is implantedbetween two adjacent vertebrae V₁ and V₂, the opening 420 is filled withbone or bone promotion substances and the electrical promotion of bonegrowth causes bone of the adjacent vertebrae V₁ and V₂ to grow into andthrough the vertical opening 420 into that bone or bone promotingsubstances from one vertebra V₁ to the other vertebrae V₂.

As shown in FIGS. 12 and 13, the control circuitry 470 and the powersupply 460 are contained within the central chamber 436 of the housing430 such that the EBGP implant 410 is a self-contained unit. The wirecoil 426 is coupled directly to a cathode lead 472 such that the wirecoil 426 becomes negatively charged.

As shown in FIGS. 11 and 14, alternatively, the control circuitry 470and power supply 460 may be implanted in an area of the patient's bodyremote from the EBGP implant 410. The cathode lead 472 may be coupleddirectly to the wire coil 426 via lead wire 462 or may be coupled to thebody of the housing 430 which is electrically conductive, and the wirecoil 426 may also be electrically coupled to the housing 430 so that thehousing 430 becomes electrically charged. However, it is preferred thatthe wire coil 426 be connected to either a wire coil such as describedabove in reference to FIGS. 9 and 10 or threads 200 as described abovein reference to FIGS. 7, 8A and 8B. In this manner, efficient use of thepower supply 460 is made as the drain is reduced without diminishing theeffectiveness of the electrical promotion of bone growth as discussedabove.

Referring to FIGS. 16 and 17 a fifth alternative embodiment of the EBGPimplant 510 of the present invention is shown. The EBGP implant 510comprises a housing 530 having a non-electrically conductive cap 550threaded to its distal end 538, and a remotely implanted power supply560 and control circuitry 570 connected to the housing 530. As the cap550 is non-conductive, the housing 530 itself is negatively charged whencoupled to the cathode lead 572 and the cap 550 has no electricalcharge. The power supply 560 is electrically connected to the housing530 by the lead wire 562 which terminates at a connector 590 which isattached by a screw 592 to the housing 530.

It is appreciated that a remotely implanted power supply and/or relatedcontrol circuitry may be used to deliver electric current to any of theembodiments described above that are self-contained units having aninternal power supply and generator, without departing from the scope ofthe present invention.

Referring to FIGS. 18 and 19 a sixth alternative embodiment of the EBGPsystem 612 of the present invention is shown. In the sixth alternativeembodiment, the EBGP implant 610 comprises an electromagnetic fieldtransmitter 600 that is worn external to the patient's body. Thetransmitter 600 has two portions 602 and 604 which are secured to thepatient's body by a band 606 or any other suitable means, such that eachportion 602, 604 is placed on opposite sides of the body at the exteriorof the patient's body.

Implanted between two adjacent vertebrae V₁ and V₂ of the patient is ahousing 630 similar to the housing 30 described above. The housing 630is at least in part ferromagnetic and thereby capable of beinginductively coupled to the electromagnetic fields transmitted by thetransmitter 600. The EBGP implant 610 thereby may be inductively coupledto transmitter 600 and in this manner electromagnetic fields andresultant induced electrical currents in EBGP implant 610 may beconcentrated and directed to a location in which bone growth is desiredwithout the need for surgically implanting a power supply and/or controlcircuitry within the housing 630 or within the body of the patient. Thenon-ferromagnetic portion of the housing 630 also may be electricallyconductive, which would make the housing 630 capable of beinginductively coupled to the electromagnetic fields transmitted by thetransmitter 600 as well as a conductor of electrical currents induced bysaid externally applied electromagnetic fields.

Similarly, if a rechargeable power supply 460 (FIG. 12) is containedwithin the housing 630, the power supply may be recharged with theapplication of external electromagnetic fields via the transmitter 600.Thus, the power supply in implant 610 could be much smaller in size asthe power supply may be repeatedly recharged. In this manner, both thehousing 630 and the power supply therein may be inductively coupled tothe transmitter 600, such that the housing 630 delivers electricalcurrent to the adjacent bone mass and the power supply is beingrecharged. After the transmitter 600 is no longer inductively coupled tothe EBGP implant 610 the replenished power supply in implant 610continues to deliver electrical current to the housing 630. In thismanner, the period of time in which a patient must wear the transmitteris substantially reduced to the period of time required to replenish thepower supply, while maintaining a continuous delivery of electricalcurrent to the housing 630.

As a further alternative, a rechargeable power supply may be implantedremote to the spine, preferably subcutaneously, such that the powersupply is easily rechargeable via electromagnetic induction. Theinductive coupling of a subcutaneous power supply with theelectromagnetic transmitter 600 overcomes the problems of infectionassociated with any direct coupling of a power supply to a power source.Further, subcutaneous implantation of the power supply also facilitatesexplantation of the power supply and further reduces the risk ofinfection to the patient. In contrast to implantations in other areas ofthe body.

Referring to FIG. 20 a seventh alternative embodiment of the EBGPimplant 710 of the present invention is shown. In the seventhembodiment, the housing 730 has a substantially rectangular hollowconfiguration and has a tapered distal end 738. The housing 730 has anupper surface 750 and a parallel lower surface 752 and two side walls754 and 756. The housing 730 has a series of small openings 742 throughthe upper and lower surfaces 750 and 752 and through the side walls 754and 756 for permitting bone growth there through. Contained within thespinal implant 710 are the power supply 760 and the control circuitry770 so that the spinal implant 730 is a self-contained unit. The powersupply 760 and/or control circuitry 770 are electrically coupled to thehousing 730 by a cathode lead 772 and an anode lead 774. The anode lead774 is coupled to an insulating screw 790 having an electricallyconductive core 796. The insulating screw 790 is threaded into the EBGPimplant 710 and insulates the anode lead 774 from the rest of the EBGPimplant 710.

Referring to FIG. 21 an eighth alternative embodiment of the EBGPimplant 810 of the present invention is shown. The EBGP implant 810 ismuch like the seventh alternative embodiment except that the housing 830has a hollow rectangular configuration with raised engagement teeth 880for engaging the bone of adjacent vertebra V and has a wire 850 similarto wire 350 described above, coiled about the housing 830. The wire 850is insulated from the housing 830 by an insulating material 864 having agroove 862 for receiving the wire 850. The insulating material 864 isidentical to insulating material 364 discussed above. The EBGP implant810 is also a self-contained unit as the power supply 860 and/or thecontrol circuitry 870 are contained within the hollow chamber of thespinal implant 810 and are electrically coupled to the wire 850.

It is appreciated that the EBGP implant of the present invention is notlimited to use in the spinal fusion process but is also applicable topromoting almost any fusion of a large joint and for promoting healingof a fracture of any of the major bones of the body. Furthermore, theapparatus and method of the present invention may be incorporated intovarious total knee arthroplasty and total hip arthroplasty. Suchimplants may embody the above-described teachings without departing fromthe scope of the present invention. Such implants may be wholly orpartially electrically conductive having a permanent or rechargeablepower supply and related control circuitry located within the implantitself such that the implant is a self-contained unit. The use of arenewable power source is of great advantage with such implants in thatthe bone fusion process, or the healing of the larger bones such as thefemur or hip, for example, may require a longer period of time for bonehealing fusion than the service life of the implantable permanent powersupplies that are presently utilized. As discussed above in greaterdetail, the recharging of the power source through external charging canextend the delivery of electrical current to the site in which inductionof osteogenesis is desired for a substantially greater period of time.

Further, such implants may also comprise externally appliedelectromagnetic coils to generate an electromagnetic field that may beinductively coupled to the implant which in turn delivers electricalcharges to the areas of bone adjacent to the implant as described ingreater detail above and recharge the power supply by electromagneticinduction from an externally applied electrical field. All of suchimplants have the added advantage in that once implanted they becomepermanently entombed within the bone fusion mass after completion of thefusion process and need not be surgically removed.

While the present invention has been described in detail with regards tothe preferred embodiments, it is appreciated that other variations ofthe present invention may be devised which do not depart from theinventive concept of the present invention.

1. An implant for promoting bone growth between at least two adjacentbone masses, said implant comprising: opposed first and second surfacesadapted for placement between and in contact with the adjacent bonemasses, a mid-longitudinal axis, and a hollow chamber between the firstand second surfaces, the hollow chamber being adapted to hold bonegrowth promoting material, the hollow chamber being along at least aportion of the mid-longitudinal axis of the implant, each of the firstand second surfaces having at least one opening in communication withthe hollow chamber into which bone from the adjacent bone masses grows;and an energizer including a cathode and an anode, the energizer beingcoupled to the implant and configured to energize the implant to promotebone growth from adjacent bone mass to adjacent bone mass through thefirst and second surfaces and through at least a portion of the hollowchamber at the mid-longitudinal axis of the implant.
 2. The implant ofclaim 1, wherein the energizer is at least in part within the hollowchamber of the implant.
 3. The implant of claim 1, wherein the energizeris at least in part between the first and second surfaces of the implantthat are placed between and in contact with the adjacent bone masses. 4.The implant of claim 1, wherein the energizer is configured to energizethe implant from a point external to a patient's body.
 5. The implant ofclaim 1, wherein the energizer is configured to provide a negativecharge to a first portion of the implant.
 6. The implant of claim 1,wherein the energizer is configured to provide a positive charge to asecond portion of the implant to inhibit bone growth in an area adjacentto the second portion.
 7. The implant of claim 1, wherein the energizeris configured to deliver of one of an alternating current, a directcurrent, and a sinusoidal current.
 8. The implant of claim 1, whereinthe energizer includes one of an electromagnetic wave generator, anelectromagnetic energy generator, and a magnetic field generator.
 9. Theimplant of claim 1, wherein the energizer includes an electromagneticfield generator adapted to be positioned external to a patient's bodyand inductively coupled to the implant.
 10. The implant of claim 1,further comprising a coil wrapped around at least a portion of theimplant, the coil being electrically conductive.
 11. The implant ofclaim 10, wherein at least a portion of the coil is in the form of anexternal thread on at least a portion of the first and second surfacesof the implant.
 12. The implant of claim 1, further comprising a passagebetween at least two of the openings through the implant such that thepassage communicates with each of the adjacent bone masses to be joined,and having a conductive coil disposed about the passage and adapted tobe coupled to the energizer.
 13. The implant of claim 1, wherein thefirst and second surfaces of the implant are at least in part arcuate.14. The implant of claim 1, wherein the implant comprises bone growthpromoting material.
 15. The implant of claim 1, wherein the implant iscombined with bone growth promoting material.
 16. The implant of claim15, wherein the bone growth promoting material includes at least one ofbone morphogenetic protein and hydroxyapatite.
 17. The implant of claim1, wherein the implant is combined with a material that intrinsicallyparticipates in the growth of bone from one of the adjacent bone massesto the other of the adjacent bone masses.
 18. The implant of claim 1,wherein the implant is an interbody spinal fusion implant.
 19. Theimplant of claim 1, wherein the implant is adapted for fusion of a jointin the body.
 20. The implant of claim 1, wherein the adjacent bonemasses are vertebral bodies.
 21. The implant of claim 1, wherein theadjacent bone masses are broken portions of the same bone.
 22. Theimplant of claim 1, wherein the anode and the cathode of the energizerare spaced apart from the opposed first and second surfaces of theimplant.
 23. The implant of claim 1, wherein the energizer is configuredto deliver a negative electrical charge and a positive electrical chargeto the implant.
 24. The implant of claim 1, wherein the energizercomprises a power supply and control circuitry.
 25. The implant of claim1, wherein at least a portion of the energizer includes non-conductivematerial.